Method of in-situ-retorting oil shale

ABSTRACT

This specification discloses a method of forming a single-well in-situ-recovery system within a nuclear chimney formed in an oil shale formation and a method of in-situ-retorting oil shale within the chimney. A nuclear explosive is positioned at the lower portion of a well and detonated to form the nuclear chimney which is filled with rubblized oil shale. A bit is connected to casing and advanced through the rubblized oil shale to form a cased well extending to the lower extremity of the chimney. The casing is then perforated and a single-well in-situ-retorting process is carried out.

United States atent 3,342,257 9/1967 Jacobs et a]. 166/247 3,465,819 9/1969 Dixon 166/299 X 3,478,825 11/1969 Closmann 166/299 3,483,730 12/1969 Gilchrist et a1. 166/251 X 3,502,372 3/1970 Prats 166/247 X 3,537,528 11/1970 l-lerce 166/247 3,542,131 11/1970 Walton 166/299 X Primary Examiner-Stephen J. Novosad Attorneys-William J. Scherback, Frederick E. Dumoulin,

William D. Jackson, Henry L. Ehrlich, Andrew L. Gaboriault and Sidney A. Johnson ABSTRACT: This specification discloses a method of forming a single-well in-situ-recovery system within a nuclear chimney formed in an oil shale fonnation and a method of in-situ-retorting oil shale within the chimney. A nuclear explosive is positioned at the lower portion of a well and detonated to form the nuclear chimney which is filled with rubblized oil shale. A bit is connected to casing and advanced through the rubblized oil shale to form a cased well extending to the lower extremity of the chimney. The casing is then perforated and a single-well in-situ-retorting process is carried out.

B I I ..p.. X. 15 I FIG.4

PATENTEUunv 16 Ian DEAN P. NICHOLS LLOYD K. STRANGE INVENTORS 423/ BY ATTORNEY ii'ii PATENTEUNUV 1s ISTI 3.620.301

I sum 2 or 2 DEAN F. NICHOLS LLOYD K. STRANGE INVENTORS ATTORNEY METHOD OF lN-SITU-RETORTING OIL SHALE BACKGROUND OF THE INVENTION This invention relates to the recovery of hydrocarbons from a nuclear chimney formed in an oil shale formation.

Nuclear explosives have been used for forming cavities in oil shale formations, which cavities are partially filled with fragmented or rubblized oil shale. These partially filled cavities are generally referred to as chimneys. In-situ-retorting processes have been carried out in these chimneys to convert the kerogen contained in the oil shale into hydrocarbons and to recover the hydrocarbons. For example, in U.S. Pat. No. 3,342,257 to Robert B. Jacobs et al. there is described a method for recovering oil from subsurface oil shale and similar formations in which an underground retort is constructed in the formation and filled with a supply of crumbled shale. This underground retort is constructed by drilling an access well into the formation and detonating a nuclear device in the well near the bottom of the formation. Thereafter gas inlet conduits are drilled into the upper portion of the cavity and oil recovery conduits are drilled downwardly alongside the cavity and then drilled directionally to connect with the lower portion of the cavity. This method of drilling oil recovery conduit outside of the cavity is followed because, as pointed out by Jacobs, the crumbled rubblelike shale in the cavity is incapable of providing lateral support for the drill stem. In situ combustion is initiated in the underground retort to convert the kerogen in the oil shale to hydrocarbons which are recovered through the oil recovery conduit.

Canadian Pat. No. 784,022 to Manley L. Natland utilizes a nuclear explosive for fonning a cavity for hydrotreating and recovering petroleum from subsurface oil-bearing formations. Natland describes a particular oil recovery tubing string which is used within a wellbore casing that extends downwardly to the lower perimeter of the cavity. This casing has perforations therethrough along the entire section penetrating the formation and the cavity.

In U.S. Pat. No. 3,465,819 to Rod P. Dixon there is recognized the problem of a excessive channeling which occurs in carrying out an in-situ-retorting process in a nuclear chimney. Excessive channeling causes a large part of the shale rubble to be bypassed by the hot combustion gases which convert by destructive distillation the kerogen of the shale into fluid hydrocarbons. Dixon solves the problem by detonating a nuclear device below the bottom boundary of the oil shale formation, thereby creating a large cavity into which only a limited amount of rubblized shale is caved. A chimney is thus formed which contains a permeable layer of limited depth of shale to be treated. This shale is then retorted in situ. Thereafter a new limited layer of rubblized shale is dropped down on the burned-out later by forcing conventional explosives into fractures in the formation above the cavity and detonating the explosives to cave another layer of fragmented shale, about to 50 feet, down onto the hot ash remaining after the previously described retorting operation.

SUMMARY OF THE INVENTION In accordance with this invention a well is provided through formations overlying a nuclear chimney and communicates with the upper portion of the chimney. This well is extended into the chimney by forcing casing having a drill bit connected to the lower end thereof through rubblized oil shale in the chimney thereby pulverizing the oil shale with the bit. A gaseous drilling fluid is circulated down the casing and upwardly through the well annulus surrounding the casing whereby the pulverized oil shale is entrained in the drilling fluid. A layer of the pulverized oil shale is deposited over the upper surface of the rubblized oil shale within the chimney.

In accordance with other embodiments, perforations are provided in the casing. A combustion-supporting gas is injected therethrough, and the layer of pulverized oil shale is ignited. In jection of the combustion-supporting gas is continued, the rubblized oil shale in the chimney is ignited, and an in situ retort is carried out to produce hydrocarbons.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic crosssectional view of a well penetrating an oil shale formation and containing a nuclear explosive device at the lower portion thereof;

FIG. 2 is a schematic cross-sectional view of a well penetrating the top of a nuclear chimney;

FIG. 3 is a schematic cross-sectional view illustrating the formation of a cased well through rubblized oil shale within a nuclear chimney; and

FIG. 4 is a schematic cross-sectional view of a single-well insitu-recovery system operated in accordance with an in-situretorting method of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated in FIG. 1 there-is provided a well 1 which extends from the surface of the earth 3 through overburden 5 and into or below an oil shale formation 7. Well 1 may be drilled, for example, by rotary-drilling techniques and cased with casing 2 which is bonded to the formations adjacent the well by cement 4. A nuclear explosive device 9 is positioned at the lower extension of well 1 and connected through detonating means 11 to the surface. Well 1 is stemmed to prevent venting to the surface upon detonation of nuclear explosive 9. This may be accomplished by positioning a suitable material such as cement 13 in the well and allowing it to set.

Upon detonation of nuclear explosive 9, a nuclear chimney 16 is formed as shown in FIG. 2. The force and temperature resulting from the nuclear explosion are so great that the oil shale formation 7 in the vicinity of the explosion is vaporized, forming a spherical cavity (not shown) therein. Around the cavity there exists a zone of molten oil shale which primarily settles to the lower portion of the cavity and solidifies into a solidified zone 6. Solidified zone 6 is highly impermeable and contains a major portion of the radioactive material resulting from the nuclear explosion. Beyond the molten zone, fractures 14 are created in the oil shale. Upon the subsequent reduction of pressure within the cavity the unsupported fractured oil shale overlying the cavity begins crumbling and caves into it thereby forming nuclear chimney 16 which is partially filled with rubblized oil shale 17. The rubblized oil shale varies in size from small pieces to blocks up to several feet across. Nuclear chimney 16 is only partially filled with rubblized oil shale, there being a void or slump zone 19 at the upper portion thereof. The oil shale initially nearest the roof of the cavity is fractured into the smallest pieces and falls to the bottom thereof followed by larger fractured pieces. Thus, the character of the rubblized oil shale 17 filling nuclear chimney l6 grades from large blocks at the upper zone to small pieces at the bottom thereof.

Thereafter, well 1 is redrilled (not shown) through stemming 13 to provide communication into nuclear chimney 16. A cased hole 21, as shown in FIG. 3, is extended through rubblized oil shale 17 to the lower portion of nuclear chimney 16 and terminates above solidified zone 6. This cased hole 21 is formed by attaching to the lower end of casing 23 a bit 25 having fluid passageways 27 therethrough. The casing and bit are then forced through rubblized oil shale 17 and gaseous drilling fluid 29 is circulated down casing 23 and back up annulus 24 between casing 23 and hole 26. Casing 23 and bit 25 may be rotated to aid in forming hole 26 through rubblized oil shale 17. The action of bit 25 upon rubblized oil shale 17 further fragments and pulverizes it, and circulating gas 29 removes the pulverized oil shale from the path of the bit. As circulating gas 29 passes void 19, the velocity of the gas stream decreases and much of the pulverized oil shale settles over surface 18 of rubblized oil shale 17, thus depositing layer 31 of pulverized oil shale. Retrievable drill collars (not shown) may be used inside casing 23 to provide the rigidity and stability necessary to maintain safe drilling conditions through the rubblized zone.

The extending of well 1 and forming of cased hole 26 through rubblized oil shale 17 in the above manner enables hole 26 to be maintained open through rubblized oil shale l7 and to be cased with the desired size casing 23 even though rubblized oil shale 17 does not have sufficient stability to allow casing of a desired size to be run by conventional techniques. The use of gaseous drilling fluid 29 removes the rubblized oil shale or drill cuttings produced in forming hole 26 without wetting rubblized oil shale 17, thus maintaining rubblized oil shale 17 in condition for retorting. Most important the use of a gaseous drilling fluid is the means by which layer 31 of pulverized oil shale is deposited over the surface 18 of rubblized oil shale 17. Thus, in initiating an in-situ-combustion process, layer 31 of pulverized oil shale may be readily ignited which in turn ignites the larger blocks of oil shale forming the upper surface 18 of rubblized oil shale 17.

First perforations 33 are provided in casing 23 at a location adjacent the upper surface 18 of rubblized oil shale 17. In addition, second perforations 35 may be formed in the lower portion of casing 23. A back-off joint 37 may be positioned a sufficient distance above bit 25 so that it will be located within well 1 above void 19 when cased hole 21 is extended to the lower portion of nuclear chimney 16. Thereafter, the remaining part of the drilling string above back-off joint 37 may be removed from well 1, thus conserving casing.

An in-situ-retorting process carried out in accordance with an embodiment of this invention is described with reference to FIG. 4. A cased well is provided in a nuclear chimney as was described with reference to FIG. 3. A combustion-supporting gas is injected through perforations 33, and layer 31 of pulverized oil shale is ignited which in turn ignites rubblized oil shale 17. Ignition may be facilitated for example be setting a packer (not shown) in casing 23 below perforations 33, lowering a device such as an electric heater (not shown) to approximately the location or perforations 33, injecting the combustion-supporting gas through casing 23 and by the electric heater, whereby the gas is heated to a temperature greater than 400 F., and then injected through perforations 33. The hot gases thus bring about ignition of the pulverized oil shale layer 31 which in turn ignites rubblized oil shale 17. It is extremly important that perforations 33 be provided adjacent the upper surface 18 of rubblized oil shale 17. As shown in FIG. 4, this upper surface 18 is covered by the pulverized oil shale layer 31. Thus, by injecting the heated combustion-supporting gas through perforations 33 at this location, the pulverized oil shale layer 31 is ignited and burns over the surface 18 of rubblized oil shale 17. This in turn ignites rubblized oil shale 17 across its upper surface 18 and thereby initiates uniform burning of rubblized oil shale 17. Injection of combustion-supporting gas is continued and a direct drive burning front 47 is established which moves downwardly through rubblized oil shale 17. if a heater has been lowered down casing 23 to initiate combustion it may be removed and tubing string 43 run to near the bottom of hole 26 and production packer 45 set in the annulus between tubing string 43 and casing 23 to facilitate recovery of hydrocarbon products therefrom. As the combustion front 47 moves downwardly through rubblized oil shale 17 the kerogen of the oil shale is retorted thereby forming liquid and gaseous hydrocarbons. These hydrocarbons move downwardly through rubblized oil shale l7 and are produced through fluid passageways 27 of bit 25 and perforations 35 of casing 23, and thence upward through tubing string 43 to the surface where they are recovered.

It is highly important that combustion front 47 move uniformly downwardly through rubblized oil shale 17. This minimizes bypassing portions of rubblized oil shale l7 and maximizes recovery of hydrocarbons therefrom. Thus, in accordance with an embodiment of this invention, the combustion front is monitored and thereafter controlled to obtain this uniform movement. This monitoring may be done for example by running a temperature survey from within casing 23 and usually from within tubing string 43. For example, a continuously recording thermosensitive device may be lowered down casing 23 or tubing string 43 while the temperature is simultaneously observed at the surface of the earth. By thus monitoring the progress of combustion front 47 and controlling the volume and pressure of the in ected combustionsupporting gas, a uniformly downward progression of corn bustion front 47 through rubblized oil shale 17 is obtained and the recovery of hydrocarbon from nuclear chimney 16 is maximized.

What is claimed is:

l. A method of providing a cased well in a nuclear chimney in a subterranean oil shale formation and having rubblized oil shale therein, comprising:

a. drilling a well through the formations overlying said chimney and communicating with the upper portion of said chimney;

b. extending said well into said chimney by advancing a bit through said rubblized oil shale thereby pulverizing said oil shale with said bit and advancing casing through said well as it is drilled;

c. concomitantly with step a circulating a gaseous drilling fluid down said casing and upwardly through the well annulus surrounding said casing whereby said pulverized oil shale is entrained in said drilling fluid; and

d. depositing a layer of pulverized oil shale over the upper surface of said rubblized oil shale within said chimney.

2. A method of recompleting a well in a nuclear chimney having rubblized oil shale therein, said well containing stemming material above said chimney, comprising:

a. drilling through the stemming material in said well to provide communication with said chimney;

b. extending said well and forming a cased hole through said rubblized oil shale to the lower portion of said chimney by advancing a bit through said rubblized oil shale thereby pulverizing said oil shale with said bit and advancing casing through said well as it is drilled;

c. concomitantly with step b circulating a gaseous drilling fluid down said casing and upwardly through the well annulus surrounding said casing whereby said pulverized oil shale is entrained in said drilling fluid; and

d. depositing a layer of pulverized oil shale over the upper portion of said rubblized oil shale within said chimney.

3. The method of claim 2 further comprising:

a. forming first perforations in said casing adjacent the upper surface of said rubblized oil shale; and

b. forming second perforations in the lower portion of said casing.

4. An in-situ-retorting method wherein a well is completed in accordance with claim 2, comprising:

a. injecting a combustion-supporting gas through first perforations provided in the casing adjacent the upper surface of said rubblized oil shale;

b. initiating combustion of the layer of pulverized oil shale;

c. continuing the inject the combustion-supporting gas to form a direct drive burning front downwardly through said rubblized oil shale; and

d. producing hydrocarbons through second perforations provided in the lower portion of said casing.

5. The method of claim 4 comprising the further step of monitoring said burning front.

6. The method of claim 5 wherein said burning front is monitored by sensing the temperature in said well. 

2. A method of recompleting a well in a nuclear chimney having rubblized oil shale therein, said well containing stemming material above said chimney, comprising: a. drilling through the stemming material in said well to provide communication with said chimney; b. extending said well and forming a cased hole through said rubblized oil shale to the lower portion of said chimney by advancing a bit through said rubblized oil shale thereby pulverizing said oil shale with said bit and advancing casing through said well as it is drilled; c. concomitantly with step b circulating a gaseous drilling flUid down said casing and upwardly through the well annulus surrounding said casing whereby said pulverized oil shale is entrained in said drilling fluid; and d. depositing a layer of pulverized oil shale over the upper portion of said rubblized oil shale within said chimney.
 3. The method of claim 2 further comprising: a. forming first perforations in said casing adjacent the upper surface of said rubblized oil shale; and b. forming second perforations in the lower portion of said casing.
 4. An in-situ-retorting method wherein a well is completed in accordance with claim 2, comprising: a. injecting a combustion-supporting gas through first perforations provided in the casing adjacent the upper surface of said rubblized oil shale; b. initiating combustion of the layer of pulverized oil shale; c. continuing to inject the combustion-supporting gas to form a direct drive burning front downwardly through said rubblized oil shale; and d. producing hydrocarbons through second perforations provided in the lower portion of said casing.
 5. The method of claim 4 comprising the further step of monitoring said burning front.
 6. The method of claim 5 wherein said burning front is monitored by sensing the temperature in said well. 